The present invention is generally related to the field of image projection systems, and more particularly to the use of transparent screens adapted to have at least switchable portions, said switchable portions capable of switching from a transparent to a translucent condition.
When projecting an image in an audience space, the aim is to give the image formed on a projection screen a homogeneous and large brightness in a limited part of the audience space, viz. only in the space where the audience is present. In this way the available radiation energy can be optimally utilized for the image observed by the audience. The part of the space where the audience is present is, however, a relatively limited part and has different dimensions in the vertical and horizontal directions. In the horizontal direction the viewing angle should be as large as possible, whereas the vertical viewing angle is generally much smaller. To realize the different viewing angles, the image projection screen may be provided with means which ensure a horizontal spread and means which ensure a vertical spread of the light.
In the context of using a projection screen for projecting, e.g., advertising information, the drawbacks associated with conventional screens are manifold and readily apparent. Such screens are large, bulky, costly, and take up much space that could readily be used for many other purposes. Moreover, such screens are adapted for an image to be projected onto only one side of the screen, and the back side is useless. Ideally, one would like to take advantage of space that was already being used for other purposes, and employ that space for projecting advertising purposes at appropriate times. One such space that answers to this description is glass windows. Windows in, for example, commercial retail establishments take up large amounts of real estate, but have relatively limited functionality. While true that windows do provide the function of letting light in and allowing patrons to look inside, at times when the establishment is closed, the windows function as no more than a barrier to outside elements. Unfortunately, windows cannot be employed as the screen onto which information, e.g., advertising, can be projected. The reasons for this are readily appreciated: glass is transparent, and hence an image projected onto it is not xe2x80x9cheldxe2x80x9d on the glass, but rather passes through it.
In general, projection screens are opaque screens, which light cannot pass through. Projection screens are generally classified into a front projection screen (reflection type) and a rear projection screen (transmission type). The rear projection screen is very useful because it enables one to compactly constitute a projection apparatus for simply projecting a film for slide, microfiche, 8 mm and 16 mm cinefilms. In addition, the rear projection screen is also useful as a large scale screen for video projectors which draw attention in this information oriented age.
Heretofore, most rear projection screens have been so-called coating type screens which are produced by coating a transparent or semitransparent support with a pigment, glass powders, synthetic resin spheres, aluminum metal powders and the like dispersed in a vehicle. Other types of rear projection screens having some other advantages, i.e. rear projection screens utilizing light scattering effect caused by crystalline particles formed in a crystalline high polymer material, are also known, for example, as shown in Japanese Utility Model Publication No. 14236/1968 and Japanese Patent Publication No. 192574/1973.
One of the principle drawbacks associated with projection screens of any type are the relatively large amounts of space they occupy, both in terms of wall space and floor space. For example, conventional projection screens have dimensions of approximately five feet square. While such screens may be stored, even such portable screens are large, bulky, and not easily moved.
Alternatively, stationary screens, such as the larger screens that mechanically retract into the ceiling of a room, are both expensive, and subject to periodic malfunction, usually in times of greatest need. In such situations, a presenter is usually forced to project images onto a bare wall which may be covered by dark colored paint or patterned wallpaper. In either situation, the resulting image is, at best, of poor quality.
Accordingly, there exists a need for a new type of projection screen that takes advantage of the large areas of space already available in many commercial establishments. This new type of projection screen and related system should be highly reliable, not needing to us the bulky mechanical systems of the prior art. Moreover, such a system should be relatively inexpensive, and allow the user multiple applications. These and other advantages of the system will be described in detail hereinbelow.
The present invention addresses the foregoing need by providing a projection screen made of glass or some other transparent material, such as plastic, having one or more switchable portions. The switchable portions may be switched from a transparent mode to an opaque mode and vice versa. When in the transparent mode, an image projected thereon will merely pass through. However, when in the opaque mode, the image projected from a projector onto the screen will be reflected by the opaque portion of the screen.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.